It is well known that toughening agents such as grafted rubbers can be employed to improve the toughness of polyamides. See generally, U.S. Pat. No. 4,174,358 assigned to E.I. DuPont de Nemours & Co. It is also well known that glass fibers can be incorporated into such polyamide blends to increase their stiffness. Such a product has been available from DuPont for a number of years, under the name ZYTEL® 80G33HS1L BK104. It is also well known that plasticized polyvinylbutyral can be used as a toughener in, for example, 6-nylon. See generally, U.S. Pat. No. 5,770,654 also assigned to E.I. DuPont de Nemours & Co and directed to such compositions suitable for a variety of applications where good toughness is required, as in packaging subjected to rough handling. As used herein polyvinylbutyral is abbreviated as “PVB”.
Plasticized PVB can be difficult to handle as a feed to a compounding extruder due to its inherent stickiness. Similarly PVB sheet is a material that can be difficult to work with because of the tendency to adhere to itself. Sheets of PVB can stick together, or bind, with such strength that it is very difficult to separate the layers. The irreversible nature of this self-adhesion by PVB is referred to in the art of PVB manufacture as “blocking”. Once PVB “blocks”, process difficulties are encountered. This tendency to block can make manufacturing processes that incorporate PVB unnecessarily complex and difficult. Consequently, continuous processes in which PVB is handled either in sheet form or in small shredded pieces can be very expensive to run, and therefore are not practical.
Moreover, blends of PVB sheet or small shredded pieces with other materials can block in the same manner as homogenous PVB compositions. Such blends of PVB with other polymers can be difficult to obtain in a cost-effective manner. A preferred process for preparing blends of PVB with other polymers would utilize conventional loss-in-weight screw feeders, which are found throughout that industry.
Recent work in the field indicates that blends of PVB with polyethylene and grafted rubbers are sufficiently non-sticky that they can be fed into a compounding extruder. See for example, WO 02/12356 of E.I. DuPont de Nemours & Co., directed to a process for preparing pellets from PVB scrap material.
It is an object of the present invention to provide PVB-toughened, glass filled polyamides that are suitable for conventional processing techniques. A feature of the invention is usefulness in fabricating a wide range of molded articles. It is an advantage of the present invention to provide polyamide-based compositions and blends that resist blocking, making them more attractive candidates for commercial applications. These and other objects, features and advantages of the present invention will become better understood upon having reference to the following description of the invention herein.